The direct amination of benzene was first proposed in 1917 and since then efforts have been made to increase the conversion of this reaction limited by thermodynamic equilibrium. Best results reported until 2007 are presented in documents U.S. Pat. Nos. 3,919,155, 3,929,889, 4,001,260, and 4,031,106 from Dupont, which reveal a catalyst of Ni/NiO/ZrO2 whose oxygen from nickel oxide reacts with the hydrogen formed in the amination, yielding water. This catalyst is regenerable after a chemical reaction. The reaction system allowed obtaining a conversion of about 13%, operating at 300° C., and at 300 bar.
Document WO 2007/025882 from BASF, describes the use of a palladium or palladium alloy membrane catalytic reactor to conduct the direct amination of benzene. A process is described, in which hydrogen is removed from the reaction system under the influence of the partial pressure difference between retentate (reaction medium) and permeate. To the permeate is applied a current of cleaning gas or even oxygen, with which the permeated hydrogen reacts, thus maintaining its partial pressure very low on the permeate side. According to the inventors, this system allows increasing the conversion of benzene to aniline in 20%.
Document WO 2011055343 describes an electrochemical reactor for direct amination of benzene, with electrochemical pumping of oxygen or hydrogen. This type of reactor is equipped with a ceramic electrolyte conductor of ions (of hydrogen or oxygen) and impermeable to non-ionic species. The purposed reactor works similarly to a fuel cell, where the oxidizing and reducing reactions occur in the electrodes located on both sides of the electrolyte. The configuration of this type of reactor is used to selectively supply oxygen to or remove hydrogen from the catalytic zone of the direct amination of benzene.
Fuel cells that use ceramic electrolytes are denominated solid oxide fuel cells (SOFC). These cells have gained special interest since they present advantages over other types of fuel cells (e.g., cells with polymeric electrolyte).
A solid electrolyte can operate at higher temperatures, thus favouring the kinetics of the chemical and electrochemical reactions, they can operate with direct feeding of hydrocarbons (with or without internal reforming), they are more stable mechanically, and they are chemically compatible with carbon monoxide. The first solid electrolytes proposed for fuel cells were composed of zirconium oxide stabilized with yttrium oxide (yttria stabilized zirconia—YSZ). These electrolytes, based on ceramic conducting oxygen ions are, still today, the most frequently used in solid oxide fuel cells, as they present a good ionic conductivity, are mechanically resistant, and are compatible with oxidising and reducing atmospheres. However, they have the drawback of their optimal operation temperature laying close to 800° C. [1, 2].
The development of new electrolytes based on the conduction of hydrogen ions has gained great support in recent years. Electrolytes based in cerium oxide have been replacing YSZ, as they allow lowering the operation temperature of the SOFC to about 500° C. Most common known electrolytes are those consisting of barium cerates doped with yttrium (yttria doped barium cerate—BCY). Those materials present considerable protonic conductivity values and a temperature lower than 600° C. Due to its characteristics this type of materials are most interesting for processes where separation and formation of hydrogen are necessary [1, 2].